Modern Very Large Scale Integrated (VLSI) chips require cooling to improve reliability of their circuitry and interconnects, to increase their circuit switching performance, and to regulate thermally generated noise in their circuits. Cooling reduces the likelihood that a metal wire will form voids or a contact will become open. It also reduces the extent of time-dependent transistor mobility and threshold degradation which adversely affects circuit performance and operation. Furthermore, in typical complementary metal oxide semiconductor (CMOS) microprocessors, every reduction in temperature of 10.degree. C. produces a 2% rise in operating frequency. For CMOS transistors, high temperatures yield significantly larger leakage currents, due to the thermal generation of carriers. This deleterious current doubles every 11.degree. C. and is known to adversely affect the functional operation of dynamic and analog circuits.
As VLSI circuits shrink to improve performance and increase operating frequencies, higher amounts of heat are generated, for example, due to constant switching of these devices. The removal of heat within a semiconductor chip structure thus becomes a major obstacle to the efficient performance of the device. Therefore, a need continues to exist for enhanced heat removal techniques for semiconductor devices.
In addition to the continued reduction in chip size, new materials are being incorporated to increase circuit performance. For example, dielectric materials with a dielectric constant (k) lower than that of conventional oxide reduce the parasitic capacitance between neighboring conductors, thereby improving circuit speed. However, most low k dielectrics are also lower in density than silicon oxide, and exhibit lower thermal conductivities as well thus further increasing the need for enhanced heat removal techniques.